Methods and apparatus for switching a transponder to an active state, and asset management systems employing same

ABSTRACT

A transponder that may be used as an RFID tag includes a passive circuit to eliminate the need for an “always on” active RF receiving element to anticipate a wake-up signal for the balance of the transponder electronics. This solution allows the entire active transponder to have all circuit elements in a sleep (standby) state, thus drastically extending battery life or other charge storage device life. Also, a wake-up solution that reduces total energy consumption of an active transponder system by allowing all non-addressed transponders to remain in a sleep (standby) state, thereby reducing total system or collection energy. Also, the transponder and wake-up solution are employed in an asset tracking system.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/963,773 entitled Methods and Apparatus for Switching a Transponder toan Active State, and Asset Management Systems Employing Same” filed Dec.9, 2010, now U.S. Pat. No. 8,022,826, which is a divisional of U.S.patent application Ser. No. 11/678,296 entitled “Methods and Apparatusfor Switching a Transponder to an Active State, and Asset ManagementSystems Employing Same” filed Feb. 23, 2007, now U.S. Pat. No.7,876,225, which claims the benefit of U.S. Provisional Application No.60/776,046, entitled “Methods and Apparatus for Switching a Transponderto an Active State, and Asset Management Systems Employing Same,” whichwas filed on Feb. 23, 2006, the disclosure of which is incorporatedherein by reference.

GOVERNMENT CONTRACT

This work was supported in part by a grant from NASA under Contract No.NNK040AZ9C. The United States government may have certain rights in theinvention described herein.

FIELD OF THE INVENTION

The present invention relates to transponders, such as RFID tags, and inparticular to methods and apparatus for switching a transponder to anactive state and asset managements system that employ such transponders.

BACKGROUND OF THE INVENTION

The use of radio frequency identification (RFID) systems is expandingrapidly in a wide range of application areas. RFID systems consist of anumber of radio frequency tags or transponders (RFID tags) and one ormore radio frequency readers or interrogators (RFID readers). The RFIDtags include one or more integrated circuit (IC) chips, such as acomplementary metal oxide semiconductor (CMOS) chip, and an antennaconnected thereto for allowing the RFID tag to communicate with an RFIDreader over an air interface by way of RF signals. In a typical RFIDsystem, one or more RFID readers query the RFID tags for informationstored on them, which can be, for example, identification numbers, userwritten data, or sensed data. RFID systems have thus been applied inmany application areas to track, monitor, and manage items as they movebetween physical locations.

RFID tags can generally be categorized as either passive tags or activetags. Passive RFID tags do not have an internal power supply. Instead,the relatively small electrical current induced in the antenna of apassive RFID tag by the incoming RF signal from the RID reader providesenough power for the IC chip or chips in the tag to power up andtransmit a response. Most passive RFID tags generate signals bybackscattering the carrier signal sent from the RFID reader. Thus, theantenna of a passive RFID tag has to be designed to both collect powerfrom the incoming RF signal and transmit (or reflect, e.g., backscatter)the outbound backscatter signal. Due to power limitations, the abilityto provide devices such as sensors or microprocessors on passive RFIDtags is limited. Passive RFID tags do, however, have the advantage of anear unlimited lifetime as they obtain their power from the RF signalsent from the RFID reader.

Active RFID tags, on the other hand, have their own internal powersource, such as, without limitation, a battery, a fuel cell or what iscommonly known as a super capacitor. The internal power source is usedto power the IC chip or chips and discrete circuit elements, whichtypically include an RF receiver, an RF transmitter, and some type ofcontroller, such as microcontroller or other processor, and any otherelectronics provided on the active RFID tag. As a result, active RFIDtags can include relatively high power devices such as sensors,microprocessors, receivers and transmitters. Also, because of theon-board power, active RFID tags typically have longer ranges and largermemories than passive RFID tags. The internal power source, however,also means that active RFID tags typically have a lifetime that islimited by the lifetime of the power source. Thus, periodic maintenanceis required.

As noted above, multiple active RFID tags may be used to track, monitor,and manage multiple items/assets as they move between physicallocations. In such an application, each active RFID tag is affixed to anitem/asset that is located in a particular location or environment, suchas in a building. Building shall refer to any structure including,without limitation, a warehouse, a hospital, an office building, or evena vehicle. In current RFID systems, the active RFID tags, when deployedin such a manner, are done so in a state where (i) an RF receiver of thetag is in an active state for receiving RF signals, and (ii) thecontroller is in a low power inactive (sleep) state to preserve power.When one or more of the active RFID tags are to be queried, the RFIDreader sends out a wake-up signal that is received by the RF receiver ofeach tag. Tags may also be on continuously not requiring a wake-upsignal. Upon receipt of the signal, the RF receiver in each tag willthen send a signal to the controller of the tag that causes it to movefrom the inactive state to an active (wake-up) state. For example, inRFID systems implemented according to the ISO 18000 Part 7 standard,when one or more tags are to be queried, the reader will send out a 30KHz tone lasting for a period of approximately 2.5 seconds. Upon receiptof the tone, the RF receiver in each tag will wake-up the controller inthe tag. The RFID reader then sends out signals intended for particularones of the tags. Those particular tags for which the signals areintended will then perform the requested action, and the remaining tags(i.e., those tags not currently of interest to the reader) will moveback to a sleep state.

The multiple active RFID tag arrangement just described presents atleast two power management problems. First, each active RFID tag that isdeployed is required to have at least one component, i.e., an RFreceiver, in an active, relatively high power consuming state at alltimes so that it can listen for the wake-up signal. Second, when theRFID reader needs to query one or more particular tags, all of the tagsthat are deployed are woken up (for example, according to the ISO 18000,Part 7 standard), i.e., their controllers are caused to move to anactive, relatively high power consuming state. Only when a particulartag determines that the query in question is not intended for it will itthen move back to the sleep state. As will be appreciated, theseproblems result in unnecessary use of power from the power source (e.g.,battery) of each tag, and therefore decreases the lifetime of each tag.

SUMMARY OF THE INVENTION

The present invention overcomes at least two problems associated with(1) current active RFID tags, and (2) current active RFID tag wake-upprotocols. The first problem is that in current RFID tags, an active RFreceiving element must always be awake to anticipate a wake-up signalfor the balance of the tag electronics. The present invention uses apassive circuit to eliminate the need for an “always on” active RFreceiving element to anticipate a wake-up signal for the balance of thetag electronics. This solution allows the entire active RFID tag to haveall circuit elements in a sleep (standby) state, thus drasticallyextending battery life or other charge storage device life and thusessentially eliminating shelf maintenance on the active RFID tag. Thesecond problem is that in current active RFID tag systems, theelectronics of all of the RFID tags in a system are awakened in responseto wake-up signals even if the signal is not intended for a particulartag or tags. The present solution provides a major energy saving circuitthat eliminates the need to wake up all of the RFID tags in response toeach wake-up signal. This circuit thus reduces total energy consumptionof an active RFID tag (or sensor) system or collection of devices byallowing all non-addressed tags (sensors) to remain in a sleep (standby)state, thereby reducing total system or collection energy. This secondcircuit can be used in conjunction with the first passive circuitmentioned above or in conjunction with any existing active RFID tag(sensor) systems. Thus, the elements of the present invention capitalizeon the benefits of an active RFID tag while eliminating the problemsdiscussed above, thus moving active RFID tags closer to a passive tagoperation.

In one embodiment, the present invention relates to a transponderapparatus, such as, without limitation, an RFID tag, that includes anelectronic device, such as a processing unit (e.g., microprocessor ormicrocontroller), that is capable of being in an inactive, sleep stateand an active state, a power source, such as a battery, in electroniccommunication with the electronic device for providing power to theelectronic device, and a switch having an antenna for receiving at leastone RF signal. The switch converts the at least one RF signal into atleast one DC signal. The at least one DC signal causes the electronicdevice to move from the inactive, sleep state to the active state.Preferably, the switch does not require power from the power source oranother power source within or connected to the transponder apparatus.The switch may, in one embodiment, include a rectifying circuit, such asa charge pump, for converting the at least one RF signal into the atleast one DC signal. The switch in that embodiment may also furtherinclude a matching network electrically connected to the antenna,wherein the charge pump is electrically connected to an output of thematching network. In yet another embodiment, the transponder apparatusmay further include an RF transmitter and/or an RF receiver that is/arein electronic communication with the processing unit.

In one particular embodiment, the antenna is tuned to a particularfrequency or range of frequencies. In this embodiment, the at least oneRF signal has a frequency that is substantially equal to the particularfrequency or is within the range of frequencies.

The at least one DC signal may be provided to the electronic device todirectly cause the electronic device to move from the inactive, sleepstate to the active state. Alternatively, the transponder apparatus mayfurther include a filtering circuit in electronic communication with theswitch, wherein the at least one DC signal is provided to the filteringcircuit. The filtering circuit provides a wake-up signal to theelectronic device to cause the electronic device to move from theinactive, sleep state to the active state only if the at least one DCsignal and/or the at least one RF signal has a predetermined format,such as a predetermined number of bursts each having a predeterminedduration.

In another embodiment, the transponder apparatus further includes one ormore additional switches that each has an additional antenna forreceiving at least one additional RF signal. Each additional switchconverts the at least one additional RF signal into at least oneadditional DC signal. The at least one RF signal and each of the atleast one additional RF signals have different frequencies. In thisembodiment, a logical combination of the at least one DC signal and oneor more of the at least one additional DC signals causes the electronicdevice to move from the inactive, sleep state to the active state.Alternatively, the electronic device may be caused to move from theinactive, sleep state to the active state only if the at least one DCsignal and the at least one additional DC signals are created in aparticular sequence.

In another embodiment, the present invention relates to a method ofmoving an electronic device, such as a processing unit, included in atransponder apparatus from an inactive, sleep state to an active state,wherein the electronic device consumes power from a power source of thetransponder apparatus in the active state. The method includes receivingat least one RF signal and converting the at least one RF signal into atleast one DC signal without consuming power from the power source oranother power source within or connected to the transponder apparatus.The method further includes providing a wake-up signal to the electronicdevice in response to receipt of the at least one RF signal that causesthe electronic device to move from the inactive, sleep state to theactive state. The wake-up signal of the method may, in one particularembodiment, be the at least one DC signal. Alternatively, the method mayinclude determining whether the at least one DC signal or the at leastone RF signal has a predetermined format, wherein the providing stepcomprises providing the wake-up signal (which is separate from the atleast one DC signal) to the electronic device to cause the electronicdevice to move from the inactive, sleep state to the active state onlyif it is determined that the at least one DC signal or the at least oneRF signal has the predetermined format. The predetermined format mayinclude a predetermined number of bursts, each of the bursts having apredetermined duration.

In another embodiment, the method further includes receiving at leastone additional RF signal and converting the at least one additional RFsignal into at least one additional DC signal without requiring theconsumption of power from the power source or another power sourcewithin or connected to the transponder apparatus. In this embodiment,the at least one RF signal and each of the at least one additional RFsignals have different frequencies, and the providing step comprisesproviding the wake-up signal to the electronic device to cause theelectronic device to move from the inactive, sleep state to the activestate only in response to a logical combination of the at least one DCsignal and one or more of the at least one additional DC signals.Alternatively, the wake-up signal may be provided to the electronicdevice only if the at least one DC signal and the at least oneadditional DC signals are created in a particular sequence and/or if theat least one RF signal and each of the at least one additional RFsignals are received in a particular sequence.

Another aspect of the present invention relates to a system for trackinga plurality of assets that includes a central computer system thatmaintains a plurality of records relating to the assets, and a pluralityof transponders, wherein each of the transponders is associated with arespective one of the assets and stores an identifier identifying theparticular asset with which it is associated. Each of the transpondersincludes an electronic device capable of being in an inactive, sleepstate and an active state, a power source in electronic communicationwith the electronic device for providing power to the electronic device,and a switch having an antenna for receiving at least one RF signal thatis generated at the direction of the central computer system. The switchconverts the at least one RF signal into at least one DC signal thatcauses the electronic device to move from the inactive, sleep state tothe active state. When the electronic device is in the active state, thetransponder generates and transmits a response signal including theidentifier identifying the particular asset with which the transponderis associated. The response signal is then used to update a particularone of the records maintained by the central computer system relating tothe asset identified by the identifier in the response signal.Preferably, the switch in each of the transponders does not requirepower from the power source of the transponder or another power sourcewithin or connected to the transponder. The transponders may be any ofthe various embodiments described above. As such, individualtransponders or groups of transponders may be selectively awakened.

In one particular embodiment, the system further includes a network withwhich the central computer system may communicate, a plurality ofwireless access points in electronic communication with the network, anda plurality of interface devices. Each of the interface devices isadapted to (i) wirelessly communicate with at least one of the wirelessaccess points, (ii) receive the response signal transmitted by aparticular one or more of the transponders, and (iii) generate andtransmit to the at least one of the wireless access points at least onesecond response signal that includes each identifier that was includedin each response signal received by the interface device. Each at leastone second response signal is transmitted to the central computer systemthrough the network. The central computer system uses the at least onesecond response signal received from one or more of the interfacedevices to update one or more of the records.

In another particular embodiment, the system further includes a networkwith which the central computer system may communicate, and a pluralityof interface devices. Each of the interface devices is adapted to (i)communicate with the network, (ii) receive the response signaltransmitted by a particular one or more of the transponders, and (iii)generate and transmit to the network, through a wired or wirelessconnection, at least one second response signal that includes at leasteach identifier that was included in each response signal received bythe interface device. Each at least one second response signal istransmitted to the central computer system through the network, and thecentral computer system uses the at least one second response signalreceived from one or more of the interface devices to update one or moreof the records.

In either of these two just described embodiments, the assets arelocated within an environment such as one or more building (e.g., ahospital), and each of the interface devices may be associated with aparticular location within the environment. In addition, each of thesecond response signals may include an identification of the interfacedevice from which it was transmitted, and the central computer systemmay use the identification included in each second response signal toupdate in the records a location of one or more of the assets.

In one particular embodiment, each of the transponders has a codeassociated therewith, and wherein for each of the transponders in orderfor the at least one RF signal received by the transponder to beconverted in at least one DC signal that will cause the electronicdevice of the transponder to move from the inactive, sleep state to theactive state, the at least one RF signal received by the transpondermust be formatted according to the code associated with the transponder.In another particular embodiment, each of one or more groups of selectedones of the transponders have a code associated therewith, and whereinfor each of the groups of transponders in order for the at least one RFsignal received by each transponder in the group to be converted into atleast one DC signal that will cause the electronic device of thetransponder in the group to move from the inactive, sleep state to theactive state, the at least one RF signal received by the transponder inthe group must be formatted according to the code associated with thegroup of transponders. Thus, individual transponders or groups oftransponder may be selectively awakened.

In an alternative embodiment, the present invention relates to a systemfor tracking a plurality of assets that includes a central computersystem maintaining a plurality of records relating to the assets, anetwork, wherein the central computer system is in electroniccommunication with the network, and a plurality of interface deviceseach being adapted to communicate with the network. In addition, thesystem includes a plurality of transponders, wherein each of thetransponders is associated with a respective one of the assets andstores an identifier identifying the particular asset with which it isassociated. Each of the transponders is adapted to receive from one ofthe interface devices at least one RF signal that is generated at thedirection of the central computer system and in response thereto togenerate and transmit a response signal including the identifieridentifying the particular asset with which the transponder isassociated. Each of the interface devices is adapted to (i) receive theresponse signal that is transmitted by each of a particular one or moreof the transponders, and (ii) generate and transmit to the network atleast one second response signal that includes each identifier that wasincluded in each response signal received by the interface device. Ineach case, the at least one second response signal is transmitted to thecentral computer system through the network, and the central computersystem uses the at least one second response signal received from one ormore of the interface devices to update one or more of the records. Fora group the transponders, the at least one RF signal that is generatedat the direction of the central computer system and that causes each ofthe transponders in the group to generate and transmit the responsesignal including the identifier identifying the particular asset withwhich the transponder is associated may be common to the transponders inthe group.

The at least one second response signal in each case may be a pluralityof second response signals, wherein each of the second response signalscorresponds to a respective one of the response signals that wasreceived by the interface device and includes the identifier that wasincluded in the corresponding one of the response signals. The centralcomputer system may further be adapted to cause the generation of the atleast one RF signal particular to one or more of the transponders in asequential fashion, wherein corresponding response signals and secondresponse signals are generated and transmitted in a correspondingsequential fashion. Location information associated with each interfacedevice may be used to update the location of each of the assets asdescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description given below, serve to explain the principles ofthe invention. As shown throughout the drawings, like reference numeralsdesignate like or corresponding parts.

FIG. 1 is a block diagram of an active RF transponder according to oneembodiment of the present invention;

FIG. 2 is a schematic diagram of a burst switch according to an aspectof the present invention;

FIG. 3 is a block diagram of an RF transponder according to analternative embodiment of the present invention;

FIG. 4 is a schematic illustration of a code that may be required toawaken the transponder 50 shown in FIG. 3;

FIG. 5 is a block diagram of an RF transponder according to a furtheralternative embodiment of the present invention;

FIG. 6 is a block diagram of an alternative RF transponder that issimilar to the RF transponder shown in FIG. 1 but that further includesan RF receiver;

FIG. 7 is a block diagram of an alternative RF transponder that issimilar to the RF transponder shown in FIG. 3 but that further includesan RF receiver;

FIG. 8 is a block diagram of an RFID system according to an aspect ofthe present invention;

FIG. 9 is a block diagram of an asset management system according to afurther aspect of the present invention; and

FIG. 10 is a block diagram of an interface device forming a part of theasset management system shown in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of an RF transponder 5 according to oneembodiment of the present invention. The RF transponder 5 includes aburst switch 10, which is described in more detail in connection withFIG. 2. The burst switch 10 is in electronic communication with aprocessing unit 15, which may be, without limitation, a microprocessor,a microcontroller, or some other type of processor device. Theprocessing unit 15 may further be another type of electronic device,such as a CMOS device or any other electronic circuit element providedon, for example, a semiconductor substrate or printed circuit board(PCB), which performs a particular function or functions. The processingunit 15 is capable of being placed into an inactive, sleep state wherethe current drawn by it is at a minimum. In addition, the processingunit 15 may be woken up, i.e., moved from the inactive, sleep state toan active state, upon receipt of an external input signal. An RFtransmitter 20 is in electronic communication with the processing unit15. The RF transmitter 20 may be a separate transmitter component, ormay be part of a transceiver component that is capable of bothtransmitting and receiving RF signals. The RF transmitter 20 is, inresponse to commands received from the processing unit 15, able totransmit RF signals through an antenna 25 connected thereto. Like theprocessing unit 15, the RF transmitter 20 is capable of being placedinto an inactive, sleep state where the current drawn by it is at aminimum, and can be woken up by receipt of an external input signalprovided by the processing unit 15. The RF transponder 5 also includes abattery 30 which provides the power required for the operation of theprocessing unit 15 and the transmitter 20. The battery 30 mayalternatively be replaced by another power source, such as, withoutlimitation, a fuel cell or a super capacitor.

FIG. 2 is a schematic diagram of the burst switch 10. The burst switch10 includes an antenna 35, which, in the embodiment shown in FIG. 2, isa square spiral antenna. The antenna 35 is electrically connected to amatching network 40, which in turn is electrically connected to avoltage boosting and rectifying circuit preferably in the form of acharge pump 45. Charge pumps are well known in the art. Basically, onestage of a charge pump essentially doubles the effective amplitude of anAC input voltage and stores the resulting increased DC voltage on anoutput capacitor. The voltage could also be stored using a rechargeablebattery. Successive stages of a charge pump, if present, willessentially increase the voltage from the previous stage resulting in anincreased output voltage. The matching network 40 matches the inputimpedance of the charge pump 45 to the impedance of the antenna 35 foroptimal performance of the antenna 35 and optimal charge pump 45 outputvoltage. In one particular embodiment, the matching network 40 is an LCtank circuit formed by, for example, the inherent distributed inductanceand inherent distributed capacitance of the conducing elements of theantenna 35. The antenna 35 is tuned to receive RF signals having aparticular frequency or range of frequencies. The RF signals that arereceived by the antenna 35 are provided, in the form of an AC signal, tothe charge pump 45 through the matching network 40. The charge pump 45essentially amplifies and rectifies the received AC voltage signal andoutputs the resulting DC signal. These operations are performed withoutrequiring the consumption of power from the battery 30 or any otherpower source within or connected (physically) to the RF transponder 5.

Referring again to FIG. 1, in operation, the RF transponder 5 isdeployed in a state wherein the processing unit 15 and the transmitter20 are in the inactive, sleep state. As such, the draw on the battery 30will be at a minimum. When it is desired to “wake-up” the RF transponder5, an RF signal of an appropriate frequency is transmitted to the RFtransponder 5 by, for example, an RFID reader or other suitable device.The RF signal is received by the burst switch 10, and as describedabove, the RF signal is used to produce a DC signal. The DC signal thatis produced is provided to the sleep input (pin) of the processing unit15, which causes the processing unit 15 to move from the inactive, sleepstate to its active state. In the active state, the processing unit 15is able to perform any action that is required, such as waking up the RFtransmitter 20 and causing it to transmit a signal that containsinformation such as an identifier for the RF transponder 5. Whenfinished (or after some predetermined period of time), the processingunit 15 can return to an inactive, sleep state until subsequently wokenup as described herein. As will be appreciated, the burst switch 10 asshown in FIG. 2 is designed to produce a DC signal of an appropriatelevel for input into the sleep input of the processing unit 15 throughappropriate selection of the parameters of the antenna 25, the matchingnetwork 40 and/or the charge pump 45.

A shortcoming of the RF transponder 5 shown in FIG. 1 is that spuriousRF energy (noise) received by the burst switch 10 could inadvertentlycause the processing unit 15 to move to the active state, therebyconsuming power when not needed. Also, if a number of similar RFtransponders 5 (i.e., similar meaning the antenna 35 of each is tuned tothe same frequency or frequency range) are deployed together, an RFsignal that is transmitted by a reader will activate all of the RFtransponders 5, even if they are not all currently of interest to thereader. In other words, there is no way to selectively activate one ormore of them without also activating the remaining ones of them.

FIG. 3 is a block diagram of an RF transponder 50 according to analternative embodiment of the present invention that addresses theshortcomings of the simple RF transponder 5 shown in FIG. 1. As seen inFIG. 3, the RF transponder 50 is similar to the RF transponder 5 in thatit includes a burst switch 10, a processing unit 15, an RF transmitter20 connected to an antenna 25, and a battery 30. However, the RFtransponder 50 further includes a low power filtering circuit 55.Specifically, as shown in FIG. 3, the DC output of the burst switch 10is provided to the filtering circuit 55, and the output of the filteringcircuit 55 is provided to the sleep input of the processing unit 15. Thefunction of the filtering circuit 55 is twofold. First, the filteringcircuit 55 prevents spurious RF energy (noise) from inadvertentlycausing the processing unit 15 to move from an inactive, sleep state toan active state. Second, the filtering circuit 55 provides a mechanismby which the particular RF transponder 50 in which the filtering circuit55 is included can be selectively woken up, i.e., have its processingunit 15 selectively moved to an active state. The filtering circuit 55performs these functions by causing a wake-up signal to be sent to thesleep input of the processing unit 15 only if a particular sequence orpattern (i.e., format) of RF signals is received by the burst switch 10.

In the preferred embodiment, the filtering circuit 55 is a state machinethat will generate a wake-up signal only if a particular pre-set “code”is received from the burst switch 10, wherein the code is a particularsequence of a certain number of voltage “bursts” (i.e., voltage signalsof a certain (although possibly varying) length or duration; in thiscase, the bursts are DC signals, but bursts as used herein may alsorefer to RF signals of a certain (although possibly varying) length orduration) from the burst switch 10 each having a particular lengthexpressed as a multiple of some pre-set unit of time, such as 1millisecond. FIG. 4 shows an example of a 4 element code that may berequired to be output by the burst switch 10 and received by thefiltering circuit 55 in order for the filtering circuit 55 to generate awake-up signal for waking up the processing unit 15. In the example ofFIG. 4, the code that must be received is a 4 burst code consisting of aburst of length 5 (e.g., 5 milliseconds), followed by a burst of length2 (e.g., 2 milliseconds), followed by a burst of length 4 (e.g., 4milliseconds), followed by a burst of length 6 (e.g., 6 milliseconds).In effect, the code is 5 2 4 6. As will be appreciated, the code schemeof FIG. 4 is meant to be exemplary only, and any number of bursts of anypossible length and any base length unit of time may be used for aparticular code without departing from the scope of the invention.

In operation, the filtering circuit 55 will count (possibly on adedicated counter) the number of separate bursts received and the lengthof each burst (the length of each burst may be stored in a register orany suitable memory). When the count reaches the pre-set number, e.g.,4, the registers (or memory) are checked for the proper code (i.e., hasthe proper sequence of burst lengths been received). If the code isdetermined to be correct, the filtering circuit 55 will generate awake-up signal for the processing unit 15. As will be appreciated, therequired code may be generated by an RFID reader by generating asequence of an appropriate number of RF bursts wherein each RF burst isof a particular time. As described in connection with FIG. 2, each suchRF burst will result in a corresponding DC voltage (DC burst) beingoutput by the burst switch 10 having a length equal to the length of theRF burst. Thus, in order to generate the 5 2 4 6 code described above,an RF reader must output an RF burst having a length of 5 (e.g., 5milliseconds), followed by an RF burst having a length of 2 (e.g., 2milliseconds), followed by an RF burst having a length of 4 (e.g., 4milliseconds), followed by an RF burst having a length of 6 (e.g., 6milliseconds).

The filtering circuit 55 thus solves the noise problem by requiring aparticular sequence of RF bursts before the processing unit 15 isawakened. The filtering circuit 55 also allows a number of RFtransponders 50 to be deployed and selectively and independentlyawakened. In particular, each transponder 50 (or set of transponders 50to be grouped and awakened together) that is deployed at a location canbe provided with a unique code. In order for an RFID reader to wake up aparticular transponder 50 (or set of grouped transponders 50), the RFIDreader will need to generate the appropriate RF bursts. As analternative, any particular RF transponder 50 may be provided with morethan one code that would enable it to be awakened, wherein one code maybe used to awaken the RF transponder 50 individually, and another codemay be used to awaken it as part of a group of particular transponders50.

As seen in FIG. 3, the filtering circuit 55 is connected to the battery30 for power purposes. Preferably, the filtering circuit 55 is a deviceor component that may enter a low power sleep state. The filteringdevice 55 will remain in a sleep state until a burst is received, atwhich time it will move to an active state (the burst is the wake-upsignal), count the burst, measure its duration, and return to sleepuntil the next burst is received. As a result, minimal power is consumedby the filtering circuit 55. As will be appreciated, the filteringcircuit 55 thus may be any low power electronic device that can beturned on for a short period of time, increment a counter, measure aburst length, and then go back to sleep.

FIG. 5 is a block diagram of an RF transponder 60 according to a furtheralternative embodiment of the present invention that includes analternate arrangement for addressing the shortcomings of the simple RFtransponder 5 shown in FIG. 1, i.e., the noise problem and the inabilityto discriminate among multiple transponders. As seen in FIG. 5, the RFtransponder 60 is similar to the RF transponder 5 in that it includes aprocessing unit 15, an RF transmitter 20 connected to an antenna 25, anda battery 30. However, the RF transponder 60 includes multiple burstswitches 10A, 10B, 10C, and 10D wherein the antenna 35 of each burstswitch 10A, 10B, 10C, 10D is tuned to a different frequency or range offrequencies (although only four burst switches 10 are shown, more orless than four may be employed to suit the particular needs of theapplication in question without departing from the scope of the presentinvention). In addition, as represented by passive logic combination 65,the burst switches 10A, 10B, 10C, 10D are topologically interconnectedin manner that implements a selected logical combination, such as anAND, an OR, or any other logic operation or combination of operations.It will be appreciated that each burst switch 10A, 10B, 10C, 10D willonly output a DC signal if it receives an RF signal of the appropriatefrequency (each referred to as a “burst switch frequency” forconvenience). Thus, the passive logic combination 65 can be chosen toonly provide a wake-up signal to the processing unit 15 if a particularcombination of the burst switch frequencies is received. For example,the passive logic combination 65 could be implemented as an AND suchthat all of the burst switch frequencies must be received for a wake-upsignal to be sent to the processing unit 15. Alternatively, the passivelogic combination 65 could be implemented with a series of ANDs and ORssuch that any two, or any three of the burst switch frequencies or aparticular two or a particular three of the burst switch frequenciesmust be received for a wake-up signal to be sent to the processing unit15.

Thus, because particular burst switch frequencies must be received towake-up the processing unit 15, the arrangement shown in FIG. 5 preventsspurious RF energy (noise) from inadvertently causing the processingunit 15 to move from an inactive state to an active state. In addition,the arrangement shown in FIG. 5 may also be used to provide a mechanismby which the particular RF transponder 60 in which it is included can beselectively woken up, i.e., have its processing unit 15 selectivelymoved to an active state. Specifically, a number of transponders 60 maybe deployed with different burst switch frequencies and/or differentpassive logic combinations 65 such that an RFID reader can generateappropriate RF signals to selectively wake-up certain ones of the RFtransponders 60. For example, one RF transponder 60 could be deployedwherein all of the burst switch frequencies are required to wake it up,another RF transponder 60 could be deployed wherein a particular two ofthe burst switch frequencies are required to wake it up, another RFtransponder 60 could be deployed wherein a different particular two ofthe burst switch frequencies are required to wake it up, another RFtransponder 60 could be deployed wherein a particular three of the burstswitch frequencies are required to wake it up, and so on.

In an alternative embodiment of the RF transponder 60, instead ofproviding the passive logic combination 65, the burst switches 10A, 10B,10C, and 10D could be combined and biased with respect to one anothersuch that the burst frequencies must be received in a particular pre-setorder for a wake-up signal to be sent to the processing unit 15. In suchan arrangement, each burst switch 10 following a first one of the burstswitches 10 would require the preceding burst switch 10 to be energizedbefore it would be capable of outputting a DC signal. In this sense, thearrangement of burst switches 10A, 10B, 10C, 10D functions like anelectronic combinational lock, and as such is able to prevent noise frominadvertently waking up the processing unit 15 and is able to allow theRF transponder 60 in which it is implemented to be selectively woken-up.

FIG. 6 is a block diagram of an alternative RF transponder 5′ that issimilar to RF transponder 5 shown in FIG. 1 except that it furtherincludes an RF receiver 70 connected to an antenna 75. The RF receiver70 may be caused to move from an inactive, sleep state to an activestate by the burst switch 10 in order allow for further communicationwith the processing unit 15 via the RF receiver 70. The communicationsmay be according to an established standard, such as the ISO 18000 Part7 standard. Similarly, FIG. 7 is a block diagram of an alternative RFtransponder 50′ that is similar to RF transponder 50 shown in FIG. 3except that it also further includes an RF receiver 70 connected to anantenna 75. The RF receiver 70 in this embodiment may be caused to movefrom an inactive, sleep state to an active state by the burst switch 10and filtering circuit 55 in the manner described elsewhere herein inorder to allow for further communication with the processing unit 15 ofthe RF transponder 50′ via the RF receiver 70. Again, the communicationsmay be according to an established standard, such as the ISO 18000 Part7 standard.

FIG. 8 is a block diagram of an RFID system 80 according to an aspect ofthe present invention. The RFID system 80 includes a plurality of RFtransponders 85 deployed in a particular location, such as within abuilding. The RF transponders 85 may be, without limitation, any of theRF transponder embodiments described herein, such as RF transponder 5,RF transponder 5′, RF transponder 50, RF transponder 50′ or RFtransponder 60. The RF transponders 85 may also be an RF transponder asdescribed in co-pending U.S. provisional application Ser. No. 60/673,715entitled “Method and Device for Reducing Power Consumption of ActiveRFID Tags,” owned by the assignee of the present invention, thedisclosure of which is incorporated herein by reference, or any othertype of known or later developed suitable RF transponder. The RFIDsystem 80 further includes an interrogator unit 90 which is inelectronic communication with a host (central) computer system 95. Underthe control of the host computer system 95, the interrogator unit 90generates the RF signals (e.g., bursts) that are required to selectivelyawaken one or more of the RF transponders 85 in the manners describedelsewhere herein. Once awakened, each RF transponder 85 may simplytransmit some identifying information to the interrogator unit 90 toconfirm its presence at the location, or, in those embodiments thatpermit (e.g., RF transponders 5′ and 50′), each RF transponder 85 mayreceive further communications from the interrogator unit 90 (forexample, according to the ISO 18000 Part 7 standard) and respondaccordingly. Thus, due to the power conserving capabilities of the RFtransponder 5, the RF transponder 5′, the RF transponder 50, the RFtransponder 50′ and the RF transponder 60 described elsewhere wherein,the RFID system 80 is able to operate with minimal power consumption andtherefore an extended lifetime. In order to avoid collisions in oneembodiment, the RF interrogation response signals are transmitted one ata time in a sequential manner, such as according to an order determinedby the unique identifier of each RFID tag 110. Other collision avoidancemechanisms are also possible.

FIG. 9 is a block diagram of an embodiment of an asset management system100 according to a further aspect of the present invention. The assetmanagement system 100 enables centralized, remote location tracking of anumber of assets 105 within a particular location 115, such as, forexample and without limitation, a hospital or another environment. Theassets 105 may be any type of physical item, including both movableitems and items that are permanently or temporarily fixed in place. Forexample, in a hospital application, the assets 105 may be various typesof medial equipment, such as, without limitation, a crash cart, an EKGmachine, a wheel chair, a gurney, an oxygen dispenser, a staff member,or a patient. Each of the assets 105 has an RFID tag 110 physicallyassociated therewith, preferably by physically attaching the RFID tag110 to the asset 105. Each RFID tag 110 is preferably any of the RFtransponder embodiments described herein, such as RF transponder 5, RFtransponder 5′, RF transponder 50, RF transponder 50′ or RF transponder60.

The asset management system 100 further includes a central assetmanagement computer system 120 that is connected to a main network 125.The asset management computer system 120 may include, withoutlimitation, a PC or another suitable computing device that is providedwith one or more software applications for implementing the systemdescribed herein. As seen in FIG. 9, a number of wireless access points130 are in electronic communication, preferably wired communication,with the main network 125 and are dispersed throughout the location 115.Each wireless access point 130 is capable of receiving a signal from themain network 125, and thus from the asset management computer system120, and wirelessly transmitting that signal within a particular definedarea. In addition, each wireless access point 130 is capable ofreceiving wireless signals from within its particular defined area andtransmitting those signals to the main network 125, and thus to theasset management computer system 120. The main network 125 and wirelessaccess points 130 thus form a wireless network for the location 115. Inthe preferred embodiment, the wireless network for the location 115 is aWiFi network that is implemented according to the IEEE 802.11 family ofstandards, or another suitable standard.

The asset management system 100 also further includes a number ofinterface devices 135 that are dispersed throughout the location 115.Each interface device 135 is located within the range of at least one ofthe wireless access points 130. As described in greater detail below,each interface device 135 is capable of receiving wireless (RF) signalsfrom and transmitting wireless (RF) signals to the associated wirelessaccess point 130 according to the appropriate protocol. In addition,each interface device 135 is capable of transmitting RF signals to theRF tags 110 that are in proximity thereto and receiving RF signals fromthose RF tags 110. In particular, based upon control signals receivedfrom the asset management computer system 120 through the main network125 and the appropriate wireless access point 130, each interface device135 is capable of transmitting one or more RF signals to the burstswitch 10 of the associated RF tags 110 (in the manner or mannersdescribed elsewhere herein in connection with the embodiments of the RFtransponder 5, the RF transponder 5′, the RF transponder 50, the RFtransponder 50′ and the RF transponder 60) for purposes of causing theprocessing unit 15 of the associated RF tags 110 to move to an activestate. In addition, each interface device 135 is capable of receivingresponse signals from the associated RF tags 110 after they have beenawakened. In this respect, the interface devices 135 function like RFIDreaders or interrogators. For reasons that will be explainedhereinafter, each interface device 135 is provided with an identifierthat uniquely identifies it. Such identifiers enable the assetmanagement computer system 120 to associate each interface device 135with a particular location within the location 115, such as a particularroom or wing in a building. This may be done in the form of a tablestored by the asset management computer system 120. Thus, each interface135 can be located or found to be non-functional through the assetmanagement system 100 itself.

FIG. 10 is a block diagram of an embodiment of the interface device 135shown in FIG. 9. The interface device 135 includes a processing unit140, which may be, without limitation, a microprocessor, amicrocontroller, or some other type of processor device. The processingunit 140 is electrically connected to a power interface 145 whichprovides power thereto. The power interface 145 is adapted to be coupledto an AC source, such as a wall outlet, in order to receive an ACvoltage. The power interface 145 converts the AC voltage into a DCsignal that is suitable for use by the processing unit 140. A wirelessnetwork transceiver 150 is provided in electronic communication with theprocessing unit 140. The wireless network transceiver 150 is adapted toreceive wireless (RF) signals from and transmit wireless (RF) signals toone or more wireless access point 130 according to the appropriateprotocol, such an 802.11 protocol, using an appropriate frequency, suchas 2.45 GHz. In addition, a tag transceiver 155 is provided inelectronic communication with the processing unit 140 for enabling theprocessing unit 140 to transmit appropriate RF signals to the associatedRFID tags 110 and to receive appropriate response signals fromassociated RFID tags 110. Thus, as will be appreciated, each interfacedevice 135 functions as an interface between the two communicationssystems, i.e., the wireless network implemented by the wireless accesspoints 130 and the wireless communications links to the RFID tags 110.In an alternative embodiment, a separate (dedicated) transmitter may beprovided in each interface device 135 for sending the required signalsto the burst switch 10, and the RF transceiver 155 may be used for othercommunication with the RFID tags 110.

In one particular embodiment of the asset management system 100, each ofthe RFID tags 110 is an RF transponder 5 (or, alternatively, an RFtransponder 5′). The burst switch 10 of each of the RF transponders 5has an antenna 35 that is tuned to a particular frequency or frequencyrange, such as 433 MHz. In this embodiment, the asset managementcomputer system 120 stores one or more files, such as, withoutlimitation, one or more files in a database, that include for each asset105 an identification of the asset type (e.g., crash cart, EKG machine,etc.) and a unique identifier for the asset 105. The unique identifiermay be, without limitation, a serial number. The RFID tag 110 (i.e.,transponder 5) associated with each asset 105 stores the uniqueidentifier for the asset 105. The unique identifier may be stored in amemory of the RFID tag 110 that is part of the processing unit 15thereof or that is separate from but in electronic communication withthe processing unit 15 thereof. When deployed, the processing unit 15 ofeach RFID tag 110 is in a sleep state, and will remain in that stateuntil awakened as described below.

In operation, this particular embodiment of the asset management system100 is adapted to track and maintain an inventory of each asset 105including the particular location of each asset 105 within the location115. To do so, the asset management computer system 120 periodically oron demand generates an asset interrogation signal. The assetinterrogation signal is sent to the main network 125 and then to eachwireless access point 130. Each wireless access point 130 thenwirelessly transmits the asset interrogation signal according to theappropriate protocol, such as an 802.11 protocol. The wirelesslytransmitted asset interrogation signal is received by each interfacedevice 135 that is within the range of each wireless access point 130.In response to receipt of the asset interrogation signal, each interfacedevice 135 generates a second RF interrogation signal having a frequencythat will be picked up by the antenna 35 of the burst switch 10 of eachRFID tag 110. As described elsewhere herein, when the burst switch 10 ofeach RFID tag 110 receives the second RF interrogation signal, a DCsignal is generated that causes the processing unit 15 of each RFID tag110 to move to an active state. Each such processing unit 15 is adaptedto then cause an RF interrogation response signal of an appropriatefrequency (e.g., 433 MHz) to be generated by the associated transmitter20 in the RFID tag 110. Each RF interrogation response signal includesthe unique identifier stored by the RFID tag 110 that generated the RFinterrogation response signal. In order to avoid collisions, the RFinterrogation response signals are, in one embodiment, transmitted oneat a time in a sequential manner, such as according to an orderdetermined by the unique identifier of each RFID tag 110. Othercollision avoidance mechanisms are also possible.

The RF interrogation response signals are then received by therespective interface devices 135 (i.e., the interface device 135 that isin proximity to the RFID tag 110 that generated the RF interrogationresponse signal). Each interface device 135 compiles a list of RFinterrogation response signals that is has received, and transmits asecond interrogation response signal for the corresponding particularlocation 137 (FIG. 9) according to the chosen protocol of the wirelessnetwork that is implemented. The second interrogation response signalgenerated and transmitted by each interface device 135 will include theunique identifier of the interface device 135 and the list of RFinterrogation response signals complied by the interface device 135. Thesecond interrogation response signals are then received by theassociated wireless access points 130 and transmitted to the assetmanagement computer system 120 through the main network 125.

Upon receipt of the second interrogation response signals, the assetmanagement computer system 120 is able to update the location of eachasset 105 in its records. In particular, each second interrogationresponse signal that is received will include a list of uniqueidentifiers that, as described above, uniquely identify each asset 105.Each second interrogation response signal will also include theidentifier of the interface device 135 that sent it, thus identifyingthe location of that interface device 135. As a result, the assetmanagement computer system 120 can use this information to associate aparticular location within the location 115 with each asset 105.

As described elsewhere herein, one of the shortcomings of the RFtransponders 5 and 5′ is that they could be inadvertently awakened byspurious RF noise. This could present a problem for the embodiment ofthe asset management system 100 just described as the RFID tags 110,being RF transponders 5 or 5′ in that embodiment, could be caused toinadvertently send RF interrogation response signals in response tonoise. This problem is addressed in an alternative embodiment of theasset management system 100 in which each of the RFID tags 110 is an RFtransponder 50 (or, alternatively, an RF transponder 50′) that will beawakened by the same burst code, e.g., 5 2 4 6. In this particularembodiment, operation of the asset management system 100 is similar tothat described above. However, in this embodiment, the second RFinterrogation signal that is generated by each interface device 135 uponreceipt of the asset interrogation signal from a wireless access point130 will be an RF signal consisting of the appropriate RF burstssufficient to cause the burst switch 10 of each RFID tag 110 to createthe required burst code for the filtering circuit 55 of the RFID tag110. As described elsewhere herein, that code, when received by thefiltering circuit 55, will cause a wake-up signal to be generated forthe associated processing unit 15, which, in response, will wake-up andgenerate the appropriate RF interrogation response signal. Thus, in thisembodiment, the adverse affects of noise are minimized.

A further shortcoming of the RF transponders 5 and 5′ is that there isno mechanism for discriminating among a number of them when deployed,i.e., there is no way to selectively cause only certain ones of them torespond. As result, the embodiment of the asset management system 100that utilizes the RF transponder 5 or 5′ will be required to interrogateall of the RFID tags 110 each time an inventory update is desired, asopposed to only interrogating selected RFID tags 110 and thus selectedassets 105. As will be appreciated, while this will still gather thenecessary asset location information, it will cause battery power forcertain of the RFID tags 110 to be unnecessarily consumed.

Thus, according to a further aspect of the present invention, a furtheralternative embodiment of the asset management system 100 is provided inwhich selected ones and/or selected groups of the RFID tags 110 may beinterrogated. In this particular embodiment, each of the RFID tags 110is an RF transponder 50 (or, alternatively, an RF transponder 50′) thatmay be awakened by a burst code that is unique to that RFID tag 110. Forexample, each individual RFID tag 110 may be assigned a unique 4 elementburst code as described elsewhere herein (such as 5 2 4 6) (a 4 elementburst code is merely an example, and it should be understood that theburst code may have more or less than 4 elements). As a result, each ofthose RFID tags 110 may be selectively, individually interrogated by theasset management computer system 120 in the manner described elsewhereherein using the appropriate burst code in order to determine thecurrent location thereof. In addition, one or more of the RFID tags 110may also be adapted to be awakened by a particular burst code that iscommon to a selected group of RFID tags 110. In other words, certaingroups of RFID tags 110 (and thus certain groups of assets 105) may alsobe assigned a second burst code that may be used to awaken each of theRFID tags 110 in the group. For example, all assets 105 of type one(e.g., crash carts, or assets on floor one of a building) may beassigned the burst code 4 2 4 3, all assets 105 of type two (e.g., EKGmachines, or assets on floor two of a building) may be assigned theburst code 3 1 4 2, etc. As a result, the location of all assets 105 ina particular group, such as crash carts, can be readily determined, ifdesired, by the asset management system 100 using a single burst code.

As will be appreciated, in the embodiment of the asset management system100 just described, each asset interrogation signal that is sent by theasset management computer system 120 will need to include informationthat identifies the particular burst code that is to be used for thatinterrogation. The interface devices 135 will then use that informationto generate the appropriate second RF interrogation signals that aretransmitted. When multiple assets 105 or specified groups thereof are tobe interrogated in this manner, the asset management computer system 120will preferably generate and transmit the appropriate assetinterrogation signals in a sequential fashion in order to avoid signalcollision problems (the responses will also be sent in a similar,corresponding sequential fashion). Thus, according to an aspect of thepresent invention, the asset management computer system 120 maintains atable or similar record that links each asset 105 with the code or codesthat may be used to awaken the RFID tag 110 associated with the asset105. That same table or other record will also preferably separatelylist specified asset groups (e.g., crash cards, EKG machines, assets ina particular wing, etc.) and the common code that is assigned to eachgroup so that such common codes may be readily accessed.

In yet a further alternative embodiment of the asset management system100, each of the RFID tags 110 is an RF transponder 60 that, asdescribed elsewhere herein, is able to be awakened by a particularcombination or sequence of burst switch frequencies. This embodiment issimilar to the embodiment of the asset management system 100 describedabove that employs the RF transponders 50 or 50′, except that the burstcodes are replaced by specified combinations or sequences of burstswitch frequencies. The basic operation of the asset management system100 otherwise remains essentially the same.

The present invention therefor provides a number of embodiments of RFtransponders and assets management systems employing the same thatminimize the power that is consumed by each transponder. As a result,the lifetime of each RF transponder may be maximized.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. For example, themajority of the description contained herein describes the burst switch10 as awakening a processing unit 15. It should be appreciated that theburst switch 10 may be utilized to awaken any type of electronic devicethat is capable of entering an inactive, sleep state. Additions,deletions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as limited by theforegoing description but is only limited by the scope of the appendedclaims.

1. A system for tracking a plurality of assets, comprising: a centralcomputer system, said central computer system maintaining a plurality ofrecords relating to said assets; a plurality of transponders, each ofsaid transponders being associated with a respective one of said assetsand storing an identifier identifying a particular asset with which thetransponder is associated, wherein each of said transponders comprises:an electronic device, wherein said electronic device moveable between aninactive, sleep state and an active state; a power source in electroniccommunication with said electronic device, said power source providingpower to said electronic device; and a switch having an antenna forreceiving at least one RF signal, said at least one RF signal beinggenerated at a direction of said central computer system, said switchconverting said at least one RF signal into at least one DC signal;wherein said at least one DC signal causes said electronic device tomove from said inactive, sleep state to said active state, wherein whensaid electronic device is in said active state the transponder generatesand transmits a response signal including the identifier identifying theparticular asset with which the transponder is associated, and whereinsaid response signal is used to update a particular one of the recordmaintained by the central computer system relating to the assetidentified by the identifier in the response signal; a network, saidcentral computer system being in electronic communication with saidnetwork; a plurality of wireless access points, each of said wirelessaccess points being in electronic communication with said network; and aplurality of interface devices, each of said interface devices beingadapted to (i) wirelessly communicate with at least one of said wirelessaccess points, (ii) receive the response signal transmitted by aparticular one or more of said transponders, and (iii) generate andtransmit to the at least one of said wireless access points at least onesecond response signal that includes each identifier that was includedin each response signal received by the interface device; wherein eachat least one second response signal is transmitted to said centralcomputer system through said network, and wherein said central computersystem uses the at least one second response signal received from one ormore of said interface devices to update one or more of said records. 2.The system according to claim 1, wherein the switch in each of thetransponders does not require power from the power source of thetransponder or another power source within or connected to thetransponder.
 3. The system according to claim 1, wherein said networkand said wireless access points implement a wireless network accordingto the IEEE 802.11 set of standards.
 4. The system according to claim 1,further comprising a wired network in electronic communication with saidcentral computer system, said transponders being adapted to communicatewith said central computer system through said wired network.
 5. Thesystem according to claim 1, wherein said assets are located within anenvironment, wherein each of said interface devices is associated with aparticular location within said environment, wherein each of said secondresponse signals includes an identification of the interface device fromwhich it was transmitted, and wherein said central computer system usesthe identification included in each second response signal to update insaid records a location of one or more of said assets.
 6. The systemaccording to claim 5, wherein said environment is one or more buildings.7. The system according to claim 6, wherein said one or more buildingsincludes a hospital.
 8. The system according to claim 1, wherein thepower source in each of the transponders is a battery.
 9. The systemaccording to claim 1, wherein the electronic device in each of thetransponders is a processing unit.
 10. The system according to claim 9,wherein each of said transponders includes an RF transmitter inelectronic communication with the processing unit of the transponder.11. The system according to claim 9, wherein each of said transpondersincludes an RF receiver in electronic communication with the processingunit of the transponder.
 12. The system according to claim 1, whereinthe antenna in each of the transponders is tuned to a particularfrequency or range of frequencies, and wherein the at least one RFsignal generated at the direction of said central computer system andreceived by the antenna in each of the transponders has a frequency thatis substantially equal to said particular frequency or is within saidrange of frequencies.
 13. The system according to claim 1, wherein theat least one DC signal of the switch in each of the transponders isprovided to the electronic device of the transponder to directly causethe electronic device to move from said inactive, sleep state to saidactive state.
 14. The system according to claim 1, wherein the at leastone DC signal of each of said transponders is provided to the electronicdevice of the transponder to directly cause the electronic device tomove from said inactive, sleep state to said active state.
 15. Thesystem according to claim 1, wherein each of said transponders is anRFID tag and wherein said at least one RF signals are generated by anRFID reader device.
 16. A system for tracking a plurality of assets,comprising: a central computer system, said central computer systemmaintaining a plurality of records relating to said assets; a pluralityof transponders, each of said transponders being associated with arespective one of said assets and storing an identifier identifying aparticular asset with which the transponder is associated, wherein eachof said transponders comprises: an electronic device, wherein saidelectronic device moveable between an inactive, sleep state and anactive state; a power source in electronic communication with saidelectronic device, said power source providing power to said electronicdevice; and a switch having an antenna for receiving at least one RFsignal, said at least one RF signal being generated at a direction ofsaid central computer system, said switch converting said at least oneRF signal into at least one DC signal; wherein said at least one DCsignal causes said electronic device to move from said inactive, sleepstate to said active state, wherein when said electronic device is insaid active state the transponder generates and transmits a responsesignal including the identifier identifying the particular asset withwhich the transponder is associated, and wherein said response signal isused to update a particular one of the record maintained by the centralcomputer system relating to the asset identified by the identifier inthe response signal; a network, said central computer system being inelectronic communication with said network; and a plurality of interfacedevices, each of said interface devices being adapted to (i) communicatewith said network, (ii) receive the response signal transmitted by aparticular one or more of said transponders, and (iii) generate andtransmit to said network at least one second response signal thatincludes at least each identifier that was included in each responsesignal received by the interface device; wherein each at least onesecond response signal is transmitted to said central computer systemthrough said network, and wherein said central computer system uses theat least one second response signal received from one or more of saidinterface devices to update one or more of said records.
 17. The systemaccording to claim 16, wherein said assets are located within anenvironment, wherein each of said interface devices is associated with aparticular location within said environment, wherein each of said secondresponse signals includes an identification of the interface device fromwhich it was transmitted, and wherein said central computer system usesthe identification included in each second response signal to update insaid records a location of one or more of said assets.
 18. The systemaccording to claim 17, wherein said environment is one or morebuildings.
 19. The system according to claim 18, wherein said one ormore buildings includes a hospital.
 20. A system for tracking aplurality of assets, comprising: a central computer system, said centralcomputer system maintaining a plurality of records relating to saidassets; a plurality of transponders, each of said transponders beingassociated with a respective one of said assets and storing anidentifier identifying a particular asset with which the transponder isassociated, wherein each of said transponders comprises: an electronicdevice, wherein said electronic device moveable between an inactive,sleep state and an active state; a power source in electroniccommunication with said electronic device, said power source providingpower to said electronic device; and a switch having an antenna forreceiving at least one RF signal, said at least one RF signal beinggenerated at a direction of said central computer system, said switchconverting said at least one RF signal into at least one DC signal;wherein said at least one DC signal causes said electronic device tomove from said inactive, sleep state to said active state, wherein whensaid electronic device is in said active state the transponder generatesand transmits a response signal including the identifier identifying theparticular asset with which the transponder is associated, and whereinsaid response signal is used to update a particular one of the recordmaintained by the central computer system relating to the assetidentified by the identifier in the response signal, wherein the switchin each of the transponders includes a rectifying circuit for convertingthe at least one RF signal received by the switch into the at least oneDC signal, and wherein the rectifying circuit of the switch in each ofthe transponders is a charge pump.
 21. The system according to claim 20,wherein the switch in each of the transponders further includes amatching network electrically connected to the antenna of the switch andwherein the charge pump of the switch is electrically connected to anoutput of the matching network.
 22. A system for tracking a plurality ofassets, comprising: a central computer system, said central computersystem maintaining a plurality of records relating to said assets; aplurality of transponders, each of said transponders being associatedwith a respective one of said assets and storing an identifieridentifying a particular asset with which the transponder is associated,wherein each of said transponders comprises: an electronic device,wherein said electronic device moveable between an inactive, sleep stateand an active state; a power source in electronic communication withsaid electronic device, said power source providing power to saidelectronic device; and a switch having an antenna for receiving at leastone RF signal, said at least one RF signal being generated at adirection of said central computer system, said switch converting saidat least one RF signal into at least one DC signal; wherein said atleast one DC signal causes said electronic device to move from saidinactive, sleep state to said active state, wherein when said electronicdevice is in said active state the transponder generates and transmits aresponse signal including the identifier identifying the particularasset with which the transponder is associated, and wherein saidresponse signal is used to update a particular one of the recordmaintained by the central computer system relating to the assetidentified by the identifier in the response signal, wherein each of thetransponders further comprises a filtering circuit in electroniccommunication with the switch of the transponder, wherein the at leastone DC signal from the switch is provided to the filtering circuit, andwherein the filtering circuit will provide a wake-up signal to theelectronic device of the transponder to cause the electronic device tomove from the inactive, sleep state to the active state only if the atleast one RF signal generated at the direction of said central computersystem and received by the antenna in the transponder has apredetermined format.
 23. The system according to claim 22, wherein thepredetermined format for each of the transponders comprises apredetermined number of RF bursts, each of said RF bursts having apredetermined duration.
 24. The system according to claim 23, whereinthe predetermined format for each of the transponders is different. 25.A system for tracking a plurality of assets, comprising: a centralcomputer system, said central computer system maintaining a plurality ofrecords relating to said assets; a plurality of transponders, each ofsaid transponders being associated with a respective one of said assetsand storing an identifier identifying a particular asset with which thetransponder is associated, wherein each of said transponders comprises:an electronic device, wherein said electronic device moveable between aninactive, sleep state and an active state; a power source in electroniccommunication with said electronic device, said power source providingpower to said electronic device; and a switch having an antenna forreceiving at least one RF signal, said at least one RF signal beinggenerated at a direction of said central computer system, said switchconverting said at least one RF signal into at least one DC signal;wherein said at least one DC signal causes said electronic device tomove from said inactive, sleep state to said active state, wherein whensaid electronic device is in said active state the transponder generatesand transmits a response signal including the identifier identifying theparticular asset with which the transponder is associated, and whereinsaid response signal is used to update a particular one of the recordmaintained by the central computer system relating to the assetidentified by the identifier in the response signal, wherein each of thetransponders further comprises a filtering circuit in electroniccommunication with the switch of the transponder, wherein the at leastone DC signal from the switch is provided to the filtering circuit, andwherein the filtering circuit provides a wake-up signal to theelectronic device of the transponder to cause the electronic device tomove from the inactive, sleep state to the active state only if the atleast one DC signal has a predetermined format.
 26. The system accordingto claim 25, wherein the predetermined format for each of thetransponders comprises a predetermined number of DC bursts, each of saidDC bursts having a predetermined duration.
 27. The system according toclaim 26, wherein the predetermined format for each of the transpondersis different.
 28. A system for tracking a plurality of assets,comprising: a central computer system, said central computer systemmaintaining a plurality of records relating to said assets; a pluralityof transponders, each of said transponders being associated with arespective one of said assets and storing an identifier identifying aparticular asset with which the transponder is associated, wherein eachof said transponders comprises: an electronic device, wherein saidelectronic device moveable between an inactive, sleep state and anactive state; a power source in electronic communication with saidelectronic device, said power source providing power to said electronicdevice; and a switch having an antenna for receiving at least one RFsignal, said at least one RF signal being generated at a direction ofsaid central computer system, said switch converting said at least oneRF signal into at least one DC signal; wherein said at least one DCsignal causes said electronic device to move from said inactive, sleepstate to said active state, wherein when said electronic device is insaid active state the transponder generates and transmits a responsesignal including the identifier identifying the particular asset withwhich the transponder is associated, and wherein said response signal isused to update a particular one of the record maintained by the centralcomputer system relating to the asset identified by the identifier inthe response signal, and wherein each of the transponders furthercomprises one or more additional switches, each of said additionalswitches of the transponder having an additional antenna for receivingat least one additional RF signal generated at the direction of saidcentral computer system, said additional switch of the transponderconverting said at least one additional RF signal into at least oneadditional DC signal, wherein said at least one RF signal received bythe antenna of the switch of the transponder and each of said at leastone additional RF signals received by the one or more additionalswitches of the transponder have different frequencies, and wherein alogical combination of the at least one DC signal and one or more of theat least one additional DC signals of the transponder causes saidelectronic device of the transponder to move from the inactive, sleepstate to the active state.
 29. A system for tracking a plurality ofassets, comprising: a central computer system, said central computersystem maintaining a plurality of records relating to said assets; aplurality of transponders, each of said transponders being associatedwith a respective one of said assets and storing an identifieridentifying a particular asset with which the transponder is associated,wherein each of said transponders comprises: an electronic device,wherein said electronic device moveable between an inactive, sleep stateand an active state; a power source in electronic communication withsaid electronic device, said power source providing power to saidelectronic device; and a switch having an antenna for receiving at leastone RF signal, said at least one RF signal being generated at adirection of said central computer system, said switch converting saidat least one RF signal into at least one DC signal; wherein said atleast one DC signal causes said electronic device to move from saidinactive, sleep state to said active state, wherein when said electronicdevice is in said active state the transponder generates and transmits aresponse signal including the identifier identifying the particularasset with which the transponder is associated and, wherein saidresponse signal is used to update a particular one of the recordmaintained by the central computer system relating to the assetidentified by the identifier in the response signal, and wherein each ofthe transponders further comprises one or more additional switches, eachof said additional switches of the transponder having an additionalantenna for receiving at least one additional RF signal generated at thedirection of said central computer system, said additional switch of thetransponder converting said at least one additional RF signal into atleast one additional DC signal, wherein said at least one RF signalreceived by the antenna of the switch of the transponder and each ofsaid at least one additional RF signals received by the one or moreadditional switches of the transponder have different frequencies, andwherein the electronic device of the transponder is caused to move fromsaid inactive, sleep state to said active state only if the at least oneDC signal and the at least one additional DC signals of the transponderare created in a particular sequence.
 30. A system for tracking aplurality of assets comprising: a central computer system, said centralcomputer system maintaining a plurality of records relating to saidassets; a plurality of transponders, each of said transponders beingassociated with a respective one of said assets and storing anidentifier identifying a particular asset with which the transponder isassociated, wherein each of said transponders comprises: an electronicdevice, wherein said electronic device moveable between an inactive,sleep state and an active state; a power source in electroniccommunication with said electronic device, said power source providingpower to said electronic device; and a switch having an antenna forreceiving at least one RF signal, said at least one RF signal beinggenerated at a direction of said central computer system, said switchconverting said at least one RF signal into at least one DC signal;wherein said at least one DC signal causes said electronic device tomove from said inactive, sleep state to said active state, wherein whensaid electronic device is in said active state the transponder generatesand transmits a response signal including the identifier identifying theparticular asset with which the transponder is associated, and whereinsaid response signal is used to update a particular one of the recordmaintained by the central computer system relating to the assetidentified by the identifier in the response signal, and wherein each ofthe transponders further comprises one or more additional switches, eachof said additional switches of the transponder having an additionalantenna for receiving at least one additional RF signal generated at thedirection of said central computer system, said additional switch of thetransponder converting said at least one additional RF signal into atleast one additional DC signal, wherein said at least one RF signalreceived by the antenna of the switch of the transponder and each ofsaid at least one additional RF signals received by the one or moreadditional switches of the transponder have different frequencies, andwherein the electronic device of the transponder is caused to move fromsaid inactive, sleep state to said active state only if said at leastone RF signal and each of said at least one additional RF signals arereceived by the transponder in a particular sequence.
 31. A system fortracking a plurality of assets, comprising: a central computer system,said central computer system maintaining a plurality of records relatingto said assets; a plurality of transponders, each of said transpondersbeing associated with a respective one of said assets and storing anidentifier identifying a particular asset with which the transponder isassociated, wherein each of said transponders comprises: an electronicdevice, wherein said electronic device moveable between an inactivesleep state and an active state; a power source in electroniccommunication with said electronic device, said power source providingpower to said electronic device; and a switch having an antenna forreceiving at least one RF signal, said at least one RF signal beinggenerated at a direction of said central computer system, said switchconverting said at least one RF signal into at least one DC signal;wherein said at least one DC signal causes said electronic device tomove from said inactive, sleep state to said active state, wherein whensaid electronic device is in said active state the transponder generatesand transmits a response signal including the identifier identifying theparticular asset with which the transponder is associated, and whereinsaid response signal is used to update a particular one of the recordmaintained by the central computer system relating to the assetidentified by the identifier in the response signal, wherein each ofsaid transponders has a code associated therewith, and wherein for eachof said transponders in order for the at least one RF signal received bythe transponder to be converted in at least one DC signal that willcause the electronic device of the transponder to move from theinactive, sleep state to the active state, the at least one RF signalreceived by the transponder must be formatted according to said codeassociated with the transponder, wherein said code associated with eachof said transponders represents a predetermined number of RF bursts,each of said RF bursts having a predetermined duration.
 32. A system fortracking a plurality of assets, comprising: a central computer system,said central computer system maintaining a plurality of records relatingto said assets; a plurality of transponders, each of said transpondersbeing associated with a respective one of said assets and storing anidentifier identifying a particular asset with which the transponder isassociated, wherein each of said transponders comprises: an electronicdevice, wherein said electronic device moveable between an inactive,sleep state and an active state; a power source in electroniccommunication with said electronic device, said power source providingpower to said electronic device; and a switch having an antenna forreceiving at least one RF signal, said at least one RF signal beinggenerated at a direction of said central computer system, said switchconverting said at least one RF signal into at least one DC signal;wherein said at least one DC signal causes said electronic device tomove from said inactive, sleep state to said active state, wherein whensaid electronic device is in said active state the transponder generatesand transmits a response signal including the identifier identifying theparticular asset with which the transponder is associated, and whereinsaid response signal is used to update a particular one of the recordmaintained by the central computer system relating to the assetidentified by the identifier in the response signal, wherein for each ofsaid transponders in order for the at least one RF signal received bythe transponder to be converted in at least one DC signal that willcause the electronic device of the transponder to move from theinactive, sleep state to the active state, the at least one RF signalreceived by the transponder must be have a predetermined formatassociated with the transponder, wherein said predetermined formatassociated with each of said transponders comprises a predeterminednumber of RF bursts, each of said RF bursts having a predeterminedduration.
 33. A system for tracking a plurality of assets, comprising: acentral computer system, said central computer system maintaining aplurality of records relating to said assets; a plurality oftransponders, each of said transponders being associated with arespective one of said assets and storing an identifier identifying aparticular asset with which the transponder is associated, wherein eachof said transponders comprises: an electronic device, wherein saidelectronic device moveable between an inactive, sleep state and anactive state; a power source in electronic communication with saidelectronic device, said power source providing power to said electronicdevice; and a switch having an antenna for receiving at least one RFsignal, said at least one RF signal being generated at a direction ofsaid central computer system, said switch converting said at least oneRF signal into at least one DC signal; wherein said at least one DCsignal causes said electronic device to move from said inactive, sleepstate to said active state, wherein when said electronic device is insaid active state the transponder generates and transmits a responsesignal including the identifier identifying the particular asset withwhich the transponder is associated, and wherein said response signal isused to update a particular one of the record maintained by the centralcomputer system relating to the asset identified by the identifier inthe response signal, wherein each of one or more groups of selected onesof said transponders have a code associated therewith, and wherein foreach of said groups of transponders in order for the at least one RFsignal received by each transponder in the group to be converted in atleast one DC signal that will cause the electronic device of thetransponder in the group to move from the inactive, sleep state to theactive state, the at least one RF signal received by the transponder inthe group must be formatted according to said code associated with thegroup of transponders.
 34. The system according to claim 33, whereinsaid code associated with each of said groups of transponders representsa predetermined number of RF bursts, each of said RF bursts having apredetermined duration.
 35. A system for tracking a plurality of assets,comprising: a central computer system, said central computer systemmaintaining a plurality of records relating to said assets; a pluralityof transponders each of said transponders being associated with arespective one of said assets and storing an identifier identifying aparticular asset with which the transponder is associated, wherein eachof said transponders comprises: an electronic device, wherein saidelectronic device moveable between an inactive, sleep state and anactive state; a power source in electronic communication with saidelectronic device, said power source providing power to said electronicdevice; and a switch having an antenna for receiving at least one RFsignal, said at least one RF signal being generated at a direction ofsaid central computer system, said switch converting said at least oneRF signal into at least one DC signal; wherein said at least one DCsignal causes said electronic device to move from said inactive, sleepstate to said active state, wherein when said electronic device is insaid active state the transponder generates and transmits a responsesignal including the identifier identifying the particular asset withwhich the transponder is associated, and wherein said response signal isused to update a particular one of the record maintained by the centralcomputer system relating to the asset identified by the identifier inthe response signal, wherein said transponders are grouped into one ormore groups of selected ones of said transponders, and wherein for eachof said groups of transponders in order for the at least one RF signalreceived by each transponder in the group to be converted in at leastone DC signal that will cause the electronic device of the transponderin the group to move from the inactive, sleep state to the active state,the at least one RF signal received by the transponder in the group mustbe have a predetermined format associated with group.
 36. The systemaccording to claim 35, wherein said predetermined format associated witheach of said groups of transponders comprises a predetermined number ofRF bursts, each of said RF bursts having a predetermined duration.